If you are looking for thin-clients that avoid proprietary elements as much as possible, here is one solution for you.
It starts with the VIA Artigo Pico ITX computer. Get it here for $310 assembled and tested. Shipping is another $20+.
The Artigo machine I got has 512 MB of RAM -- no hard disk. My plan was to put an operating system on a USB flash/key/thumb drive and boot the Artigo from the flash drive.
To keep the flash drive from burning out quickly, because of a lot of reads and writes to the flash drive, the operating system must be completely loaded into RAM when the Artigo boots. And there has to be enough free RAM with the operating system running to provide adequate swap or scratch space for the applications to run. Needless to say, my Artigo is not a Windows Vista machine.
VIA claims that the company is Linux friendly and that there are all sorts of open-source downloads available on their web site. But, damned if I could find any help there for running Linux on my Artigo box. In fact, drivers supplied by VIA for the VIAChrome graphics processor are reportedly inferior to open-source OpenChrome drivers. So, don't look for help from VIA.
A number of Linux distros claim to be USB-bootable. But in most cases, what that means is that you can put the Live-CD version on a USB flash drive and get it to run. That is not the same as installing the distro on a USB flash drive, since a Live-CD has all sorts of drivers and hardware discovery routines that run every time the Live-CD is started. There is no simple way to obtain persistence from one Live-CD session to the next.
Also, many Live-CDs do not load themselves completely into RAM; they read/load elements from the CD if/when a user selects them. For example, OpenOffice might be loaded from one distro's Live-CD only when the user selects it.
Bottom line, most of the Linux distros are not suitable for my diskless Artigo thin client.
Two Linux distros that I have gotten to work on my Artigo box are Damn Small Linux (DSL) and Slax. Pendrivelinux.com has instructions that I used to get DSL to work. It uses the Live-CD version of DSL and persistence is obtained by a clever(?) hack. The problem is that DSL is too small; it uses an older version of the Linux kernel and it uses a "frugal" window manager (Fluxbox or JWM) that looks cheap. Users/employees won't like the look and feel of the DSL desktop.
Download the Slax distro from here. Get the file that is specifically for install on a flash drive. It loads a Live-CD version of the operating system on a flash drive, but/and it provides persistence out-of-the-box. It uses the latest kernel and it uses the KDE desktop/window manager. It works like a charm on my Artigo thin client. It looks great. It loads itself completely into RAM, leaving about 70% of the 512 MB free for swap/scratch space. SWEET!
On top of this, as a Live-CD, I can take my Slax flash drive and boot it on my PC at home for secure remote access to my business computer systems. THIS is a great, open thin-client solution!